• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권11호
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• pp.5610-5624
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• 2017

A novel scheme based on polarization modulation and the weighted fractional Fourier transform (PM-WFRFT) is proposed in this paper to enhance the physical layer security of dual-polarized satellite systems. This scheme utilizes the amplitude and phase of the carrier as information-bearing parameters to transmit the normal signal and conceals the confidential information in the carrier's polarization state (PS). After being processed by WFRFT, the characteristics of the transmit signal (including amplitude, phase and polarization state) vary randomly and in nearly Gaussian distribution. This makes the signal very difficult for an eavesdropper to recognize or capture. The WFRFT parameter is also encrypted by a pseudo-random sequence and updated in real time, which enhances its anti-interception performance. Furthermore, to prevent the polarization-based impairment to PM-WFRFT caused by depolarization in the wireless channel, two components of the polarized signal are transmitted respectively in two symbol periods; this prevents any mutual interference between the two orthogonally polarized components. Demodulation performance in the system was also assessed, then the proposed scheme was validated with a simulated dual-polarized satellite system.

• Journal of Positioning, Navigation, and Timing
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• 제11권3호
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• pp.181-189
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• 2022

The public open signals from Global Navigation Satellite System (GNSS) including Global positioning system (GPS) are used widely by many peoples in the world except for the public regulated restriction signals which are encrypted. Nowadays there are growing concerns about GNSS signal spoofing which can deceive the GNSS receivers by abusing these open services. To counter these spoofing threats, many researches have been studied including array antenna techniques which can detect the direction of arrival by means of Multiple Signal Classification (MUSIC) algorithm. Originally the array antenna techniques were developed to countermeasure the jamming signal in electronic warfare by using the nulling or beamforming algorithm toward a certain direction. In this paper, we study the anti-spoofing techniques using array antenna to overcome the jamming and spoofing issues simultaneously. First, we will present the theoretical analysis results of spoofing signal response of Minimum Variance Distortionless Response (MVDR) algorithm in array antenna. Then the eigenvector algorithm of covariance matrix is suggested and verified to work with the existing anti-jamming method. The modeling and simulation are used to verify the effectiveness of the anti-spoofing algorithm. Also, the field test results show that the array antenna system with the proposed algorithms can perform the anti-spoofing function. This anti-spoofing method using array antenna is very effective in the view point of solving both the jamming and spoofing problems using the same array antenna hardware.

• 한국인터넷방송통신학회논문지
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• 제19권2호
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• pp.73-77
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• 2019

본 논문에서는 이동형 위성단말에서 발생하는 shadowing 채널에 ARQ 기술을 적용하여 성능을 확인한다. shadowing은 위성단말이 이동하면서 생기는 신호 단절이다. 신호 단절을 보상하기 위해 신호를 재전송하는 ARQ기술을 사용할 수 있다. 위성통신에서는 송신 데이터와 ack채널에서 shadowing이 발생한다. 두 채널에서 발생하는 shadowing의 상관관계에 따라 ARQ 기술 적용 후 예상되는 전송량은 다르다. 따라서 shadowing채널에 ARQ 기술을 적용할 경우 예상되는 성능을 확인한다. 분석결과 단말이 송신할 경우와 수신할 경우 전송량의 차이를 보였고, 수식적으로 성능을 예측할 수 있음을 보였다.

• 한국위성정보통신학회논문지
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• 제4권1호
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• pp.36-44
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• 2009

본 논문에서는 위성항법신호감시국에 대한 핵심기술인 FPGA 기반의 위성항법수신기를 구현하여 갈릴레오 E1 및 E5 신호처리 동작검증 및 처리결과를 제시하였다. 성능 검증을 위해 시제품 형태의 위성항법안테나, 112MHz 샘플링 주파수 및 8비트 양자화 레벨을 제공하는 RF/IF 유니트를 이용하여 갈릴레오 시험위성인 지오베-B(GIOVE-B)로부터 E1 및 E5를 수신하여 이용하였고, 수신된 데이터에 대한 신호처리 수행을 통해, FPGA 기반의 항법수신기 모듈에서 갈릴레오 E1 및 E5 신호가 정상적으로 동작됨을 입증하였다.

• 대한원격탐사학회지
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• 제33권2호
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• pp.159-169
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• 2017

위성용 전자광학탑재체는 제한된 소모전력 및 우주방사선과 같은 사용 환경에 의해 설계부터 특별한 요구사항을 가지고 있으며, 획득 영상의 품질은 주로 GSD (Ground Sampled Distance), 신호대잡음비(SNR, Signal to Noise Ratio), MTF (Modulation Transfer Function)에 따라 좌우된다. 영상센서의 출력신호에 포함된 잡음 감소를 통한 신호대잡음비 개선을 위하여, 센서에 추가된 프리픽셀(Pre-pixel) 및 다크픽셀(Dark-pixel)을 사용하여 CDS (Corrective Double Sampling) 방식을 통해 영상센서의 잡음 성분을 포함한 오프셋 신호(Offset Signal)를 제거하는 아날로그 신호처리(ASP, Analog Signal Processor) 방법을 제안한다. 또한 센서 제어시스템에서는 영상의 불균일성 처리를 위해 제어시스템의 출력 포트별 게인(Gain), 오프셋, 및 센서의 화소별 특성을 반영한 다양한 방식에 의한 보정 방법이 적용된다. 본 논문에서는 이상 설명한 여러 가지 잡음 개선방법을 시스템 설계 및 운영에 적용하여 위성탑재용 전자광학카메라의 신호대잡음비 향상 방법을 제안하고, 실험을 통해 검증한다.

• 한국통신학회논문지
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• 제36권5B호
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• pp.566-572
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• 2011

위성 통신은 해양통신에서 중요한 통신 수단으로 활용된다. 최근 차세대 위성 통신 신호로써 대두되고 있는 이진옵셋반송파 (binary offset carrier: BOC) 신호의 동기화는 위성항법시스템에서 (global navigation satellite systems: GNSS) 신호를 복조하기 위한 가장 중요한 과정 중 하나이다. 그러나 해양 위성 통신 환경에서 BOC 신호의 동기화는 BOC 자가상관함수의 주변 첨두 발생 문제와 위성 신호의 수면 반사로 인해 발생하는 다중경로 페이딩으로 인한 어려움을 갖는다. 본 논문에서는 BOC 상관함수의 주변 첨두를 완벽히 제거하고, 다중경로 환경에서도 강인한 새로운 동기화 기법을 제안하였다. 모의실험 결과를 통하여 제안한 기법이 기존 기법들에 비해 다중경로 환경에서 강인한 성능을 가짐을 보였다.

• Journal of Multimedia Information System
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• 제5권3호
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• pp.155-162
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• 2018

Nowadays, the tracking technology of Quadrant Detector will become actual by new micro devices. Based on the past filed data of the reception experiment with COMETS satellite, we have studied on new device (AD8302, phase difference detector) was acquired and suspect its abilities. In 1998, we have developed a Quadrant Detector for mobile to track a weak signal from satellite on Ka band of COMETS. The Quadrant Detector is comprised of four dedicated feed components for reception under an environment of Nakagami - Rician fading, and one transmission and reception feed component. We were successful in receiving a 23 GHz beacon signal from ICE transponder of the COMETS and succeeded in tracking the satellite from a moving vehicle at speeds of approximately 10 ~ 20 Km/h on paved roads. In 2018, with new device AD8302, we have verified new QD system and performed a simulation, based on the past filed experiment. This new device shall be improving the tracking abilities from mobile body on the earth to the multimedia satellite.

• Journal of the Optical Society of Korea
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• 제15권3호
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• pp.278-282
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• 2011

We discuss two possible optical noise sources in an electro-optic camera loaded on a low earth orbit satellite. The first noise source was a reflection at the window for signal rays incident upon the window which is placed before the FPA plane. The second noise source came from a reflection at the surface of the FPA cell when the signal flux is not entirely absorbed. We investigate the noise generation processes for two optical noise sources, and a parametric solution is used to estimate the optical noise effects.

• 한국위성정보통신학회논문지
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• 제12권2호
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• pp.65-70
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• 2017

The structure of MMSE receiver front-ended by CMA(Constant Modulus Array) array working in CDMA forward link which is applicable to LEO spread spectrum satellite communication system is proposed. By using the despreaded pilot signal of forward link as a reference signal, the CMA array can capture multi-path signals securely even in severely faded LEO satellite channel. The remaining MAI (Multiple Access Interference) is cancelled by the cascaded MMSE receiver. Besides theoretical development, through relevant computer simulation, it is proved that the proposed system shows much better BER performance than any other possible candidate systems. As a spatio-temporal receiver mounted on a mobile vehicle, the proposed system also reduces implemental cost and complexity by adopting the simplest algorithm for its spatial and temporal domain processing.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2005년도 Proceedings of ISRS 2005
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• pp.671-674
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• 2005

Atmospheric correction over the ocean part is more important than that over the land because the signal from the ocean is very small about one tenth of that reflected from land. In this study, the Spectral Shape Matching Method (SSMM) developed by Ahn and Shanmugam (2004) is evaluated using Landsat imagery acquired over the highly turbid Saemangeum Coastal Area. The result of SSMM is compared with COST model developed by Chavez (1991 and 1997). In principle, SSMM is simple and easy to implement on any satellite imagery, relying on both field and image properties. To assess the potential use of these methods, several field campaigns were conducted in the Saemangeum coastal area corresponding with Landsat-7 satellite's overpass on 29 May 2005. In-situ data collected from the coastal waters of Saemangeum using optical instruments (ASD field spectroradiometer) consists of ChI, Ap, SS, aooM, F(d). In order to perform SSMM, we use the in-situ water-leaving radiance spectra from clear oceanic waters to estimate the the path radiance from total signal recorded at the top of the atmosphere (TOA), due to the reason that the shape of clear water-leaving radiance spectra is nearly stable than turbid water-leaving radiance spectra. The retrieved water-leaving radiance after subtraction of path signal from TOA signal in this way is compared with that estimated by COST model. The result shows that SSMM enabled retrieval of water-leaving radiance spectra that are consistent with in-situ data obtained from Saemangeum coastal waters. The COST model yielded significantly high errors in these areas.